Mr Trump also begins the process with rock-solid partisan support and a US public that is lukewarm about impeachment. It is easy for Washington insiders to overestimate the degree to which the public is paying attention.

But that can change quickly. Mr Trump’s visceral reactions to hour-by-hour developments will surely draw more eyeballs to the proceedings.

IT TOOK PLACE WHILE HE WAS PRESIDENT

But why start impeachment now rather than when the Mueller report came out in April? For two reasons.

First, Mr Trump’s alleged attempt to extort a foreign leader, Volodymyr Zelensky, Ukraine’s president, took place while he was president.

Although Robert Mueller spelt out examples of obstruction of justice since 2017, the meat of his report was about alleged Russian collusion before Mr Trump took office.

In one key respect, however, “Ukrainegate” and the Mueller report are closely linked: Both involve Russia. America’s military aid is meant to help Ukraine’s defences against Russian encroachment in its east.

THE CASE IS EASIER TO GRASP

The second reason is that the alleged corruption behind “Ukrainegate” is far easier to grasp.

If Mr Trump threatened to withhold aid to a pro-western power unless it played dirty to help him win re-election, that would break through to even the most attention-deficient swing voter.

“No one is above the law,” said Ms Pelosi. Most Americans would also agree with that.

It is another matter whether Democrats can convince enough Americans that Mr Trump, like Nixon, is a crook.

The Watergate hearings were televised live from one committee room. Ms Pelosi intends to split up the drafting of articles of impeachment between six House committees. That does not augur well for primetime clarity.

Ukrainegate was sparked by a whistleblower inside the intelligence agencies who knew the contents of Mr Trump’s call to Mr Zelensky. If the whistleblower gives public testimony, and his or her account is convincing, that could change the political climate.

Mr Mueller’s much-awaited public testimony fell flat. The immediate fate of the US republic now at least partly hangs on the strength of the story the whistleblower can tell.